Enumerating phytoplankton with an upright compound microscope using a modified settling chamber

A modified settling chamber is described which permits the use of an uprigh t compound microscope for phytoplankton enumerations. The chamber is compos ed of a 75 x 51 mm rectangular or 70 mm round-glass microslide base with a 130 mum thick piece of sheet styrene attached to the upper surface. A circu lar cell is cut into the styrene material making a 26 mm diameter chamber w hich is approximately 130-150 mum deep. Settling procedures follow Utermohl 's technique, with the use of a 0.13-0.15 mm thick coverslip (50 x 45 mm) t o cover the chamber. The overall thickness of the settling slide is 1.13 mm which does not impact on the optical requirements for most objectives, inc luding oil immersion objectives. The chamber encloses a total volume of 69- 80 mm(3). No statistical differences are observed in cell, filament or colo ny counts between the new and traditional chambers. Furthermore, count comp arisons at different cell concentrations using the new chambers give consis tent results. Thus, the resolution and availability of an upright microscop e makes the use of the new settling chamber an attractive method for phytop lankton counting, especially in teaching situations.